Because of their high cholesterol content, eggs were seen as dietary villains by many, in spite of their being sources of high quality protein, low levels of total and saturated fats, and a number of other nutritional benefits (for more on eggs, read here ). More recently, however, research has demonstrated that dietary cholesterol is not an important precursor to levels of LDL ("bad") cholesterol in the human body for most people. Thus nutritionists have been less likely to demonize egg consumption and admit that they do have substantial nutritional value.
According to a recent study in the American Journal of Clinical Nutrition, animal studies have suggested a connection between dietary cholesterol and Alzheimer's Disease (AD) types of pathologies, but this observation has not been extended to humans. Dr. Maija PT Ylilauri from the University of Eastern Finland and colleagues used data from a large Finnish heart disease study to explore the possible association of dietary cholesterol/egg consumption with the risk of dementia.
In all, about 2500 men, free of dementia at the onset of the study, were included. They were 42-60 years old, and were followed for nearly 22 years. Four years after the beginning of the study, 480 of them were tested on their cognitive performance. The diets of all the men were assessed by 4-day food records at the beginning of the study.
The investigators did not find an increased risk of dementia associated with increased egg or cholesterol intakes among the men studied. In fact, they found that egg intake was actually associated with better performances on neuropsychological testing after 4 years of follow-up. In addition, a higher egg intake was associated with some favorable health factors such as a lower risk of high blood pressure.
This study had some suggestive results, however it also had serious limitations. First, only middle-aged men from eastern Finland were included. So it's not clear to what extent these results might apply to women or other populations. Further, Finns do not typically consume large quantities of eggs. In 2004, Finns consumed an average of 129 eggs per year per capita, compared to 172 in the U.S., or 345 in Mexico. It is possible that data from countries with higher levels of consumption would show different trends. And of course the psychological testing was performed early in the study, well before most of the population might be expected to develop dementia.
Taking such caveats into account, this study, at the very least, doesn't support any negative connection between development of dementia and egg consumption.